My brother and his family recently moved to Idaho, so I decided to make them a carving of the state with my new portable Primo MPCNC. He drives all over the state as part of his job, so he is sending me lots of beautiful photos of the Rocky Mountains and rivers. Idaho has a lot of terrain!
I got the terrain map data from Mapzen. Touch Terrain from Iowa State U is another good source of heightmap data. But the Mapzen one automatically adjusts the greyscale for the highest and lowest points in your chosen region, which saves a few steps. I used VcarvePro to design it, which was not easy but much easier than previous terrain carvings I have done with Fusion360. I used a 1/4" upcut two-flute carbide endmill for the roughing and cut-out, and a tapered 0.75mm ball nose bit for the finishing passes, with something like 20% stepover. That means it took about 5.5 hours per pass. But the end result needed very little sanding. I have an album with photos of the build and lots of time-lapses of the carving, more than you ever cared to watch. Have a look!